Devising efficient methods for extracting direct current (DC) power from electromagnetic radiation has become an important necessity for a number of applications involving self-powered devices, such as Radio Frequency Identification (RFID) tags and bionic implants. The operating range of such self-powered devices has been severely limited by the failure of existing power extraction techniques to successfully extract power from radio frequency (RF) signals having relatively low power levels. The problem of extracting DC power from electromagnetic radiation has two basic parts: collecting the incident radiated power, and then converting the collected power to DC signals which are usable by the self-powered devices.
Converting RF energy from RF signals at different frequencies to DC power is a relatively difficult problem particularly when the RF signals have relatively low power levels. Fundamentally, this problem arises because frequency conversion is generally a nonlinear operation, (i.e., it is necessary to operate in the non-linear region of a non-linear device). Practical systems, however, operate at relatively low RF power levels which results in operation in the linear region of non-linear devices. In addition, nonlinear devices normally used for rectification have exponential nonlinearities with relatively large “dead zones” near the origin, i.e., nonlinear devices can be non-responsive in response to signals having voltage and current levels which are close to zero. Severe constraints can also be imposed when it is desirable to provide a self-powered device which is relatively inexpensive and environmentally robust. Such cost and environmental limitations preclude the use of exotic devices and structures.